Written by Kimi Dunbar
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Of febrile children 1-36 months diagnosed with UTI, 20% will not have pyuria on screening UA. Thus, we should be careful about requiring pyuria when considering UTI diagnosis.
No whites in the urine? Could still be a UTI…
This study evaluated the accuracy of pyuria screening tests in diagnosing urinary tract infections (UTIs) in children aged 1–36 months undergoing bladder catheterization. Using urine culture as the reference standard, five pyuria tests were compared.
- Leukocyte esterase on dipstick
- WBC count on manual microscopy using a hemocytometer (What in the world is a hemocytometer, you may ask? It’s a microscope slide with gridlines to help count cells, apparently.)
- WBC count on manual microscopy without using a hemocytometer
- Automated WBC count using flow cytometry
- Automated WBC count using digital imaging with particle recognition
Among 4,188 children, flow cytometry had the highest sensitivity at 88%. Leukocyte esterase testing had 84% sensitivity, while automated WBC counts using digital imaging reached 75% sensitivity. Sensitivity of manual count with and without a hemocytometer was only 82 and 78 respectively, so this isn’t much better. Pyuria was absent in ~20% of confirmed UTI cases, questioning its reliability as a diagnostic requirement. This affirms the retirement of AAP guidelines that recommended only sending a urine culture if pyuria was present.
LE on dipstick and automated WBC count using digital imaging are the most available automated modalities; however, neither of them have high enough sensitivities to convince me to absolutely rely on them when deciding whether I’m concerned enough to start empiric antibiotics or to obtain a urine culture.
Overall, the takeaway here is that absence or presence of pyuria, while certainly important, should not unilaterally guide our decision to obtain a urine culture.
Source
Accuracy of Screening Tests for the Diagnosis of Urinary Tract Infections in Young Children. Pediatrics. 2024 Dec 1;154(6):e2024066600. doi: 10.1542/peds.2024-066600. PMID: 39563499
